(1) Field of the Invention
The present invention relates to apparatus for providing a comparison between the levels of a pair of remotely located points and particularly to liquid type levels of the communicating vessel type. More specifically, this invention is directed to facilitating comparison of the level of a pair of spatially displaced surfaces. Accordingly, the general objects of the present invention are to provide novel and improved apparatus and methods of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for employment in the building industry. In the building and construction industries it is often necessary or desirable to compare the levels of points or surfaces which are positioned at opposite sides of a dividing wall or partition. At the present time, in making such comparison, it is common practice to employ devices which are commonly referred to as "water levels". Such devices include a pair of open topped vessels which are placed in communication via a tube which may, if necessary, function as a siphon. It is well known that the pressure in a fluid is a function of height only, and at the free surfaces is equal to the general atmospheric pressure. Therefore, the free surfaces of the liquid in all communicating vessels will be at the same height. Since the equilibrium conditions within a fluid mass are in no way altered by the shape of the vessel which contains the fluid, the level of the free surface in each leg or communicating vessel will be the same regardless of the cross-sectional area of the leg. In the building industry, it is common practice for both of the communicating vessels to be defined by a tube, which is customarily a flexible transparent plastic pipe, with water being placed in the tube and the operators taking care to prevent the formation of air bubbles.
In accordance with the principle of communicating vessels, after the "water level" has stabilized, the level of the liquid will be the same at both ends of the tube. A first operator, holding one end of the tube, will move this end so that the water will be at the reference or zero level. A second operator, positioned at the opposite side of the wall or partition from the first operator, should theoretically then be able to move the second end of the tube whereby the level assumed by the liquid at this second end will correspond to the reference level. However, in part due to deformation of the tube, the theoretically obtainable result is generally not achieved.
The "water level" devices presently in use suffer from a number of deficiencies. These deficiencies include the difficulty in filling the devices without creating air bubbles, the need for two individuals to operate the devices and the impossibility of calibrating the devices so as to permit precise measurement of levels above and below the reference level. Further deficiencies of presently available "water levels" include the necessity of employing tubes of comparatively large diameter, and thus of increased weight, in order to minimize measuring errors and the ever present danger of spillage of the measuring liquid from either end of the tube in the event of incorrect handling. An additional significant deficiency of presently available levels of the communicating vessel type resides in the sensitivity of the tube to deformation stresses which leads to significant measurement error. It is also to be noted that the transparent plastic tubes commonly in use have a tendency to become cloudy, as a result of surface abrasion and other causes, and the consequent loss of transparency makes use difficult and degrades accuracy.